Two hundred and fifty-two million years ago, a series of Siberian volcanoes erupted and sent the Earth into the greatest mass extinction of all time. As a result of this mass extinction, known as the Permo-Triassic Mass Extinction, ...

Periodic mass extinctions on Earth, as indicated in the global fossil record, could be linked to a suspected ninth planet, according to research published by a faculty member of the University of Arkansas Department of Mathematical ...

Imagine dolphins disappearing from the world's oceans as a result of prolonged climate change and slower evolution. As shocking and unlikely as such an event might be, it happened in the past to a group of marine animals: ...

(Phys.org)—Sometimes when a star collapses into a supernova, it releases an intense, narrow beam of gamma rays. Gamma-ray bursts often last just a few seconds, but during that time they can release as much energy as the ...

Long before the dinosaurs, hefty herbivores called pareiasaurs ruled the Earth. Now, for the first time, a detailed investigation of all Chinese specimens of these creatures – often described as the 'ugliest fossil reptiles' ...

Secondary sexual characteristics are features that appear at sexual maturity and distinguish the two sexes of a species. Studies of secondary sexual characteristics in a species are vital for fully understanding its behavior, ...

Stanford scientists have found that chronically low levels of oxygen throughout the oceans hampered the recovery of life after the Permian-Triassic extinction, the most catastrophic die-off in our planet's history. Also known ...

Extinction event

An extinction event (also known as: mass extinction; extinction-level event, ELE) is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:

Over 99% of species that ever lived are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land organisms.

Since life began on earth, several major mass extinctions have significantly exceeded the background extinction rate. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others as it marks the extinction of nearly all dinosaur species, which were the dominant animal class of the period. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were mass extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record.

Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the threshold chosen for describing an extinction event as "major", and the data chosen to measure past diversity.